This invention lies in the field of the flare burning of waste gases on demand. More particularly, it concerns means for controlling the flow of purge gas, to maintain sufficient pressure inside of the flare stack system so that there will be no influx of atmospheric air, such as might provide an explosive gas mixture inside of the flare stack.
Field flares for emergency relief of, and burning of, as much as 160,000#/minute of flammable gases for pressure-relief in avoidance of explosion, are parts of plants for processing petroleum, petro-chemicals and chemicals. Such flare systems are pressure-tight piping systems for conveying relieved gases to a sufficiently remote, and high enough area to allow safe burning. Because any entry of air to the flare system could create an extremely hazardous explosive condition, at a time when it is not venting, and the flow within the system is static, it is conventional practice to deliver to the flare piping system a quantity of `purge` or `sweep` gases to maintain, at all times, a slow flow of gases toward the discharge point of the flare to the atmosphere.